Various cordless electrical devices may be powered by a battery pack. Examples of such cordless electrical devices include, but are not limited to, laptop computers, cell phones, personal digital assistants, and power tools such as a drill. The battery pack may include a plurality of battery cells and power switches to allow the battery cells to either supply current (discharge operation mode) or to be charged (charge operation mode). A variety of monitoring functions may be performed by circuitry of the battery pack to maintain a safe and desired use of the battery cells. As part of this and other monitoring efforts, cell voltage levels for each battery cell may be monitored. The monitored cell voltage level may be a floating or line to line cell voltage. The floating voltage measurement may be taken across the positive and negative terminals of each battery cell. In some instances, it may be desirable to translate this floating cell voltage to a ground referenced voltage.
One conventional approach to translating the floating cell voltage to a ground referenced voltage may be to utilize a differential operational amplifier with four externally coupled resistors. However, for battery packs having two or more series connected battery cells, this conventional approach requires the use of a high voltage operational amplifier to accommodate the relatively large potential difference between the inputs of the operational amplifier. A high voltage operational amplifier may have a supply voltage between about 10 volts and 40 volts and may have larger common-mode gain and offset voltage errors as compared to a low voltage operational amplifier having a supply voltage less than or equal to about 5 volts. These errors may then need to be corrected by balancing all four resistor values in a complex calibration process that may require making fine adjustments to at least one of the four resistors.
Accordingly, there is a need for single floating cell voltage level translator circuitry that reduces voltage translation error and simplifies calibration.